Rotatable sliding-thread clamp for textile machines

ABSTRACT

Thread or yarn extending through a pair of thread guides is automatically released and subsequently automatically slidably clamped against the mouth of a passage through one of such thread guides, which mouth is adjacent to the other thread guide. The two thread guides are normally urged toward each other by a spring to maintain the clamping element in its thread-clamping position. The spring force may be overcome by positive mechanical, hydraulic, or pneumatic displacing devices to create a pressure differential to override the spring force and effect thread-releasing relative displacement of the thread guides. The clamping element may be fixed to one of the thread guides, or it may be a free ball movable into and out of thread-clamping position by gravitational force, by wedging action of cooperating inclined surfaces, or by an air stream as the thread guides are moved toward and away from each other, respectively. The thread guides are mounted for conjoint rotation to create rotation of the clamped thread and thereby impart twist to the thread.

United States Patent Hoeber et al.

[ ROTATABLE SLIDING-THREAD CLAMP FOR TEXTILE MACHINES [75] Inventors:Gerhard Hoeber, lngolstadt; Hans Landwehrkamp, Gerolfing, both ofGermany [73] Assignee: Schubert & Salzer MaschinenfabrikAktiengesellschaft, lngolstadt, Germany [22] Filed: Mar. 20, 1972 [21]Appl. No.: 236,304

[30] Foreign Application Priority Data Mar. 30, 1971 Germany 2115225[52] US. Cl 57/77.33, 57/58.89, 57/106 [51] Int. Cl...... D0lh 7/92,D02g 1/04, D01h 13/04 I [58] Field of Search 57/77.3, 77.33, 77.35,

[56] References Cited UNITED STATES PATENTS 7 1,826,354 10/1931 Henk57/58.86 X 3,177,643 4/1965 De Halleux et al 57/58.86 3,352,510 11/1967Franzen 57/58.86 X 3,410,071 11/1968 Heimes 57/58.86 X 3,490,221 1/1970Heimes et al. 57/58.86 3,492,804 2/1970 Handwckrkamp et al..... 57/58.89X

FOREIGN PATENTS OR APPLICATIONS 1,497,050 10/1967 France 57/58.861,497,288

10/1967 France 57/58.86

[ 51 July 30, 1974 62,419 6/1955 France 57/58.86 1,019,206

2/1966 Great Britain 57/58.86

Primary Examiner-John W. Huckert Assistant Examiner-Charles GorensteinAttorney, Agent, or Firm-Robert W. Beach; Ms. R. M. Van Winkle [57]ABSTRACT overcome by positive mechanical, hydraulic, or pneumaticdisplacing devices to create a pressure differential to override thespring force and effect threadreleasing relative displacement of thethread guides. The clamping element may be fixed to one of the threadguides, or it may be a free ball movable into and out of thread-clampingposition by gravitational force, by wedging action of cooperatinginclined surfaces, or by an air stream as the thread guides are movedtoward and away from each other, respectively. The thread guides aremounted for conjoint rotation to create rotation of the clamped threadand thereby impart twist to the thread.

7Claims, 4 Drawing Figures ROTATABLE SLIDING-THREAD CLAMP FOR TEXTILEMACHINESi Previous thread clamps used, for example, in connection withelectrostatic open-end spinning devices have used a ball to clamp andguide thread between the openings of a pair of resiliently-connectedadjacent thread guides in cooperation with a thread take-off devicewhich continually draws the thread past the clamps. However, if, forexample, the supply of fiber to the spinning device is interrupted tocause a discontinuity in the thread so that the thread end is drawn pastthe clamp, it has been difficult to rethread the guide means andrethreading usually requires the use of tools such as grippers or hooks.

One solution to this problem was disclosed for use with circularknitting machines in U.S. Pat. No. 3,228,213, in which a sphericalclamping unit is moved from clamping engagement with a spun thread by acontinuous air stream; This device has limited application, however,because the adjacent pair of thread guides must be fixed and disposedvertically, since gravitational force is the only means for holding theball or sphere in its clamping position.

It is therefore a principal object of the present inven-' tion toprovide a simple thread-guiding clamp which can be opened and closedautomatically without regard to the stage of textile processing.

A further object is to provide such a thread-guiding clamp arrangementwhich can be opened or closed during operation of cooperating machinery,such as a spinning machine, so that thread can be supplied to the clampat any time.

An additional important object is to provide such a clamp which willautomatically clampingly engage thread fed to the thread guides whensuch guides are moved relatively toward each other.

Another object is to provide a clamp which will not damage a thread endduring the opening and closing operation.

The foregoing objects are accomplished by having a pair of relativelymovable thread guides which are normally resiliently urged toward eachother and mounted in a further guide for movement of the thread guidesaway from each other, and by providing a clamping element locatedbetween the thread guides adjacent to the mouths of passages throughsuch guides, which element is movable into its clamping position whenthe thread guides are moved towardeach other. A thread can therefore befed to the thread clamp while the two thread guides are separated fromeach other and the clamping element is thereby disposed in a positionaway from the thread guide mouth against which it clamps. The clampingfunction is automatically resumed when the thread guides are movedtoward each other because such movement urges the clamping element backinto its clamping position.

The actuating means for effecting relative movement of the thread guidesmay be mechanical, electromagnetic or hydraulic, but the preferredconstruction utilizes a pneumatic system. If hydraulic or pneumaticguide means are used, movement of the thread guides can be effected byproviding cooperating fluid passages adjacent to the thread guides intowhich fluid may be supplied or from which fluid may be evacuated tocreate a pressure differential sufficient to override the resilientforce to separate the thread guides and move the clamping element awayfrom its clamping position.

The clamping element may be rigidly connected to one of the threadguides, but is preferably a free sphere movable by rolling alongcooperating surfaces of the adjacent thread guide ends to minimizedamage to a thread end, particularly during the reclamping operation. Bymounting the two thread guides for conjoint rotation, the presentinvention may be substituted for the twist or lay chamber in pneumaticspinning devices. For this purpose the construction of the thread guidepassage are modified in configuration as described more fully below. Theclamping arrangement of the present invention can be substituted for theclamping mechanism shown in U.S. Pat. No. 3,492,804, in connection withopen-end spinning machines, with the thread guides being moved away fromeach other in response to a thread-sensing device such as aphotoelectric cell.

FIG. 1 is a longitudinal section through one form of thread-clampingdevice according to the present invenlIlOl'l.

FIG. 2 is a longitudinal section through a modified thread-clampingdevice;

FIG. 3 is a longitudinal section through a threadclamping device similarto the type shown in FIG. 2 for use in connection with an electrostaticopen-end spinning device.

FIG. 4 is a longitudinal section through an open-end spinning device inwhich the thread clamp of the present invention forms a twist chamber.

In all applications of the present invention, as described below, thethread guide clamp is used in con nection with the creation of a genuineor false twist in a thread 1 as the thread is glidingly drawn throughthe thread clamp. In FIG. 1 the thread glide clamp is shown as includingtwo coaxially arranged generally cylindrical thread guides 2 and 3having cylindrical, aligned passages therethrough to receive thethread 1. The thread guides are normally urged toward each other byresilient means which may be in the form of a compression spring 4.Thread guide 2 is carried by a holder 42 connected to one end of thearmature 40 of an electromagnet 41. Thread guide 3 is carried by aholder 30 which is connected to the carriage of a textile machine (notshown), such as a spinning machine. The thread guides 2 and 3 arerotatively mounted in their respective holders42 and 30 by ball bearings43 and 31, respectively, so that the thread guides may turn freelyrelative to the holders. The thread guides 2 and 3 are rotatedsynchronously by a common drive shaft 20 carrying respective drivepulleys 21 and 32 connected to the thread guides by drive belts 22 and33, respectively.

A teardrop-shaped element 23 connected by a bow 24 to the thread guide 2normally engages the adjacent mouth of the passage through thread guide3, and

thereby constitutes an element of the thread clamp. In

FIG. 1 the thread glide clamp is shown in its closed position, wherebythread 1 is clamped between the clamping element 23 and the thread guide3. Consequently, the thread is rotated by rotation of the thread guides2 and 3. The compression spring 4 is selected and mounted to exertsufficient pressure to maintain clamping engagement of element 23 andguide 3 with the thread 1 while permitting the thread to be drawnthrough the clamp. To prevent damage to thread 1 as it is drawn throughthe glide clamp, element 23 and the portion of the thread guide 3 whichit engages are smooth and rounded so that the thread can glide throughthe clamp without snagging or abrasion.

To release thread 1 from the clamp, or to open the clamp for feeding athread into the thread guide passages, an electromagnet 41 is actuatedby means not shown, such as a pressure switch, to raise armature 40 inopposition to the force of spring 4 and move thread guide 2 axially awayfrom thread guide 3. The clamp element 23 is thereby moved by bow 24from engagement with the passage mouth of thread guide 3. In such openposition a thread 1 can be dropped or fed easily through the passage ofthread guide 2 past the clamp element 23 and through the passage ofthread guide 3. The electromagnet 41 is then deenergized so thatarmature 40 is released, and spring 4 urges thread guide 2 toward threadguide 3- so that the clamp element 23 is automatically returned to theclamping position shown in FIG. 1.

With the construction shown in FIG. 1 there is a possibility that theend of a thread may strike bow 24 as it is fedthrough the thread guidepassages and be damaged thereby. In open-end spinning machines such adamaged thread end may cause difficulty in restarting the spinningoperation. Consequently, the modifications shown in FIGS. 2 through 4use a ball in place-of the teardrop 23 and bow 24, which ball is freelymovable within the, hollow defined between adjacent ends of the threadguides 2 and 3.

The thread clamp of the present invention can be disposed in variouspositions, and FIG. 2 illustrates horizontally disposed thread guidepassages in which a ball 5 is caged by the adjacent ends of threadguides and 35. Such ball 5 is substituted for the clamp construction 23,24 shown in FIG. 1 and is unattached to any other object. In theexemplary form of the invention shown in FIG. 2, a fan or venting device51 is operable to partially evacuate achamber' 50 encircling sleeve 6and therebyto create a pneumatic pressure drop below atmosphericpressure. Sleeve 6 is connected to thread guide 35 to prevent theirrelative rotation, but the sleeve and guide are rotatable conjointly.Sleeve 6 is mounted in holder by ball bearing'3l and is rotated by belt22 connected to a drive shaft (not shown).

An axially movable thread guide 25 havingv an external shoulder 26 isreceived in a cavity within sleeve 6 inwardly of thread guide 35. Suchsleeve has an internal shoulder 60 spaced from and facing the threadguide shoulder 26. A compression spring 61 encircles the smaller portionof thread guide 25 and its opposite. ends bear against shoulders 26 and60, respectively, to normally urge thread guide 25 toward thread guide35. The thread guide 25 has splined-shaft connections 27, 62 and 28, 63with sleeve 6. Consequently, thread guide 25 is driven through suchconnections by sleeve 6 and is thereby turned at the same rotation speedas thread guide 35. The adjacentflared mouths of the passages throughthe thread guides are countersunk to form oppositely facingfrustoconical depressions, each having a depth no greater than theradius of the ball 5, which depressions cooperatively form a cage forthe ball.

The annular chamber 50 formed by a channel 53 encircling the sleeve 6communicates through bores 64 with an internal chamber 52 between sleeve6 and thread guide 25, in which chamber spring 61 is located. Thechamber 50 is connected by a conduit 54 with a valve 55 movable betweentwo positions. In the full-line position of FIG. 2 the valve 55 providesa passage between conduit 54 and conduit 56 connected to the ventingdevice 51. In its broken-line position the valve passage vents chamberto the atmosphere.

When the device of FIG. 2 is in normal clamping position, chamber 50 andtherefore chamber 52 are connected through valve to atmosphere.Consequently,

sleeve 6 and guides 25 and 35 are rotated by belt 22, a twist will beimparted to the thread. To open the thread glide clamp for releasing thethread, valve 55 is moved to its full-line position. The chamber 50 andgroove 52 are then partially evacuated by the suction fan 51 so that thedifferential pressure between the atmospheric pressure on the face 29 ofthread guide 25 and the reduced air pressure on shoulder 26 overridesthe force'of spring 61 pressing on such shoulder to move guide 25 awayfrom guide 35.. Therefore ball 5 is relieved from pressure by wedgingsurfaces 29 and 36 and by gravitational force is moved out of the threadpath into the position shown in FIG. 2. A thread can therefore be fedthrough the thread guide passages without interference by the clampingball.

.If desired a liquid-rather, than air or some other gas, can be used inthe pressure-reducing system 52, 50, 54, 55, 56, 51, if adequate sealsare provided between sleeve 6 and thread guide 25 at opposite ends ofchamber 52. In such case the exhaust fan 51 is replaced by a pump, andthe valve 55 in its broken-line position communicates with a containerfor liquid. When the valve is in its full-line position the pump canpump off the liquid in the chambers 52, 50 and recirculate it to thecontainer. The pump can be connected to be energized or deenergizedsimultaneously with displacement of valve 55.

' In order that the longitudinal movement of thethread guide 25 isconfined within the sleeve 6, such sleeve is of a length to extendbeyond the end of guide 25 remote from guide 35, and the sleeve borereceiving guide 25 is sufficiently longer than such guide to permitmovement of the guide within the sleeve between its thread-clamping andthread-releasing positions. In this instance the thread guide passageincludes the bore 65 in sleeve 6 coaxial with the passage through guide25. To facilitate feeding a thread along the entire length of thepassage the outer end 66 of bore 65 may be frustoconically countersunk.In addition, a frustoconical depression 29' may be provided in the endof guide 25 adjacent to bore 65. Consequently, feeding a thread throughthe bore 65 and guides 25 and 35 from right to left as seen in FIG. 2 isfacilitated. To similarly facilitate feeding a thread through the devicein the opposite direction, additional frustoconical depressions can beprovided in the outer end 36' of guide-35 and in the inner end 66 ofbore 65."

Forms'of the present invention particularly suitable for use withopen-end spinning devices are shown in FIGS. 3 and 4. A ball 5 freelymovable within the ho]- low between the thread guides is also utilizedin'these forms of invention as the clamping element. If the threadpassage is arranged vertically instead of horizontally, the ball 5 couldbe moved out of clamping engagement when the thread guides are movedapart relatively by a stream of air created by a pressure differential.Such a device is shown in FIG. 3 in connection with an electrostaticopen-end spinning machine including a pair of supply rollers 7, at leastone of which is negatively charged, and a positively chargedfibercollecting surface 70 on the outer end of the passage throughthread guide 71. The electrostatic field formed between supply rollers 7and thread guide 71 resolves sliver 11 into individual fibers 10, whichfibers are collected on the surface 70 and picked up by the rotating endof a thread 1. Rotation is imparted to the thread by the thread glideclamp mounted by bearings 31 in a holder 30.

The thread guide 71 is rigidly connected to a sleeve 72 for conjointrotation by a drive belt 22. Sleeve 72 has an internal annular rib 73 onwhich one end of the compression spring 61 bears. The other end of thisspring bears against a nut 74 threaded onto the reduced portion of asecond thread guide 75 which the spring encircles. Such nut is held inplace by a lock nut 76. Annular rib 73 is located a short distance abovethe shoulder of guide 75 formed by reducing the upper end portion ofsuch guide and is preferably undercut on its lower side adjacent to suchshoulder. The shoulder is chamfered so that the shoulder and undercutrib cooperate to form an annular groove 52 of dovetail cross section.Thread guide 75 has a spline-shaft connection 77, 78 with sleeve 72 toprevent relative rotational movement of guide 75 and sleeve 72 whilepermitting relative axial movement.

A second sleeve 67 is connected with sleeve 72 by bolts extendingthrough external annular flanges on the adjacent sleeve ends. One end ofsleeve 67 receives the lower body portion of thread guide 75 andincludes internal grooves 79 of the spline-shaft connection to threadguide 75. The opposite end of sleeve portion 67 is closed by an integralplug 68 having a bore 69 therethrough for passage of thread 1.v

The lock nut 76, which cannot turn relative to thread guide 75, has anaxial flange 57 spaced from and encircling the reduced end portion ofthe thread guide 71. Flange 57 has a radial port 58 through it, thelower tangent'of which is diametrally aligned with the clamping surfaceof guide 75. Because guide 75 and sleeve 72 are not rotatablerelatively, a bore 59 communicating with corresponding to the side offlange 57 having port 58.

In this instance the thread guide 75 is moved axially relative to sleeve72 and thread guide 71 by creation of a fluid pressure differential inthe chamber 52 between the thread guide 75 and the interior of sleeve 72and atmospheric pressure. However, instead of evacuating the chamber 52the air pressure in such chamber is increased by supplying air underpressure through conduit 54 to chamber 50 and from such chamber througha plurality of bores or an annular slot 64 through sleeve 72 to chamber52. Such high pressure air presses downward on the chamfered bodyshoulder of guide 75 to override the force of spring 61 and therebymoves such guide 75 downward away from guide 71. During such downwardmovement the bore 58 in extension 57 is momentarily aligned with bore 59in sleeve 72 so that a stream of air from chamber 50'impinges on ball 5and thereby urges it from its centered clamping position toward the leftwall of flange 57 as seen in FIG. 3.

With such an arrangement, using the ball-moving air stream, it isnecessary to interrupt such air stream before introducing a thread tothe guide passage, to prevent feathering or other damage to the threadend or interfering with feeding the thread'past such air stream into thenext thread guide passage. This is accomplished by further'movement ofguide away from guide 71. After introduction of the thread 1, the supplyof the air to chamber 52 is interrupted so that thread guide 75 is againmoved toward clamping position by spring 61. Consequently, there will beno air stream acting on ball 5 when the bores 58 and 59 are again movedin alignment. Thus by continuation of movement of guide 75 toward guide71, ball 5 is positively wedged into clamping position by the inclinedsurface of frustoconically flared adjacent end 29 of guide 71.

Pneumatic displacement of ball 5 could be utilized in other forms ofthread guide clamps according to the present invention in which thethread guide passages are disposed substantially vertically. Forexample, suction could be created to move the ball if space 50 werebeing evacuated when bores 58 and 59 are aligned. Thus it is immaterialwhether the pressure differential is created by evacuating chambers 50and 52 or by supplying air under pressure to such chambers.

Instead of using an air stream to move ball 5 in a vertically disposedthread guide, the adjacent ends of the thread guides may be constructedto cooperate for guiding the ball. Such a construction is shown in FIG.4. A lower thread guide 8 is enclosed in avertically disposed sleeve sothat such guide and sleeve are not rotatable relatively. The uppersurface 81 of guide 8 through which the mouth of the thread passageopens is inclined while the adjacent end surface of thread guide 82,threaded into or bolted to sleeve 80, is conically countersunk to form adepression 83. The axis 84 of such conical depression is disposedperpendicular to the inclined plane of surface 81 of guide 8. When thethread guide clamp is electromagnetically, hydraulically orpneumatically opened ina manner previously described, ball 5 undergravitational force will roll down the incline 81 toward the left, asseen in FIG. 4, until it engages the inner wall of sleeve 80. When theclamp is'subsequently closed, the ball 5 will be rolled back up theincline 81 to the thread passage mouth by the wedging action of theconical depression 83 as the thread guide 8 approaches guide 82.

If a thread glide clamp is used in connection with an open-end spinningdevice which .is actuated by a thread-sensing device, such a clampaccording to the present invention makes it possible to restart thespinning process automatically because 'the thread 1 is prevented frombeing drawn out of the spinning device.

One particularly effective type of thread-sensing device'and itsresponsive actuating system is shown in FIG. 4. The thread sensorincludes a light source 44 and a cooperating photoelectric cell 45 whichis connected through an amplifier 46 with a relay 47 to operate switchblade 48. Such blade in the full-line position shown in FIG. 4 connectsthe current supply line to drive motor 49. In the-broken-line positionof the blade impeller 51 is energized. So long as a thread 1 interruptsthe light beam between light source 44 and cell 45, switch blade 48 ismaintained in its full-line position to energize motor 49 to drive shaft20 and belt 22, thereby rotating the thread-clamping device. If the endof thread 1 is drawn past light source 44 so that cell 45 is energized,relay 47 is actuated to swing switch blade 48 into its broken-lineposition to energize impeller 51 and open the thread clamp so a threadend can be dropped through the thread passage to the spinning device.

The present invention can be used with various types of open-endspinning devices such as pn'eumaticallyoperated spinning rotors,rotating or fixed spinning funnels, or spinning chambers in whichindividual fibers are advanced through a medium to a freely-rotatingthread end.

FIG. 4 shows a thread glide clamp of the present invention in connectionwith a spinning chamber 9 in which fibers vattach to the end of thread 1as such thread is drawn through the clamp by'take-off rollers 12. Sliver11 is fed by rollers 7 to a horizontalfeed tube 90 which supplies fibers10 from such sliver into the side of the spinning chamber 9 in aconventional manner. The take-off tube 91 connected to the upper side ofthe spinning chamberis made of transparent mate-. rial or includes awindow between light source 44 and cell 45 located on opposite sidesthereof. The thread glide clamp is located above the take-off tube91 inplace of a conventional twist-forming chamber in a position havingsleeve'80 and thread guides 8 and 82 in axial alignment with tube 91.Sleeve 80 is mounted by ball bearings 31 on the housing 92 for thespinning chamber 9, which housing is connected to a suction conduit93-below the spinning chamber. Similar to FIG. 3, sleeve 80 has aninternal annular rib 73. Thread guide 8 has a skirt 85 below such rib,and the upper shoulder formed by the skirt is 'chamfered and cooperateswith rib 73 to define a chamber 52 of dovetail cross section.Splined-shaft connections 77, 87 and 86, 79 between sleeve 80 and skirt85 effect conjoint rotation of these components.

To improve the distribution of twist using the glide clamp of thepresent invention with an open-end spinning device, the thread passagesthrough guides8 and 82 are modified in configuration. While the majorlength of the passage 96 t hrough guide 8 and skirt 85 is concentricwith the axis of sleeve 80, the mouth 94 of such passage adjacent toball 5 is offset from such axis to form a passage portion having an axisdiverging at an acute angle from the vertical axis of sleeve 80.Similarly, the mouth 97 of the passage of guide 82 remote from ball 5 isconcentric with the sleeve axis, but mouth 95 adjacent to ball 5 isoffset from such axis, the mouths 94 and 95 being in alignment with eachother.

The sliding-thread clamps shown in FIGS. 3 and 4 impart a genuine twistto the thread 1. If the thread clamp is used by placing'it between aspinning turbine (not shown) and a pair of take-off rollers, the clampwill ere-- mouths at their openings through the thread 7 guide ends, theadjacent thread guide ends defining a hollow therebetween, resilient.means normally urging such thread guides axially toward each other, anda clamping element disposed in the hollow between such thread guideends, the improvement comprising first control means for relativelymoving such thread guides axially away from each other against the forceof such resilient means, and second control means for positively movingthe clamping elementbetween a clamping position and a position in whichthe thread passages through both of said thread guides are unobstructedby said clamping element in coordination with the movement of the threadguides toward and away from each other, respectively.

2. The clamp defined in claim 1, in which the second control meansincludes a link connecting the clamping element to oneof the threadguides for conjoint relative movement therewith.

3. The clamp defined in claim 1, in which the threadreceiving passagesthrough the thread guides are disposed. substantially vertically, theclamping element is a ball, the first control means including means forcreating a pressure differential between the hollow defined by theadjacent ends of the thread guides and a fluid receiving chamberconnected to a portion of one of the thread guides remote from thehollow, and the second control means including means for momentarilyconnecting said chamber with the hollow to provide a fluid streamimpingeable on said ball.

4. The clamp defined in claim 1, in which the thread guides are disposedone above the other, and the thread-receiving passages. are disposedsubstantially vertically, the lower thread guide having an upperinclined surface through which a mouth of the threadreceiving passagethrough such guide opens, and the upper thread guide having a lowersurface through which a mouth of the thread-receiving passage throughsuch guide opens, having a conical depression, the axis ofsaid'depression beingperpendicular to said inclined surface of the lowerthread guide.

5. The clamp defined in claim 1, in which the threadreceiving passagethrough each thread guide includes afirst passage portion remote fromthe clamping element extending axially of its thread guide and a secondpassage portion having its axis inclined-at an acute angle to the axisof its thread guide, the mouths of the inclined passage portions openinginto the hollow betweenthe thread guides and being offset from theirrespective thread guide axes and being in substantial alignment.

6. The clamp defined in claim 1, the first control means includingpneumatic means for effecting relative axial movement of the threadguides away from each other against the force of the resilient means.

7. The clamp defined inclaim 1, further comprising a sleeve, mountingmeans rigidly connecting one thread guide in said sleeve, meansconnecting the other thread guide with said sleeve for axial movementrelative to said sleeve and said one thread guide and for conjointrotation with said one thread guide and said sleeve, a firstfluid-receiving chamber externally of the sleeve, asecondfluid-receiving chamber between one thread guide means and thesleeve, means connecting said first and second fluid-receiving chambers,and means for altering the pressure of fluid in said chambers.

1. A rotatable sliding-thread clamp including two coaxially alignedthread guides each having a thread-receiving passage therethrough, suchpassages forming mouths at their openings through the thread guide ends,the adjacent thread guide ends defining a hollow therebetween, resilientmeans normally urging such thread guides axially toward each other, anda clamping element disposed in the hollow between such thread guideends, the improvement comprising first control means for relativelymoving such thread guides axially away from each other against the forceof such resilient means, and second control means for positively movingthe clamping element between a clamping position and a position in whichthe thread passages through both of said thread guides are unobstructedby said clamping element in coordination with the movement of the threadguides toward and away from each other, respectively.
 2. The clampdefined in claim 1, in which the second control means includes a linkconnecting the clamping element to one of the thread guides for conjointrelative movement therewith.
 3. The clamp defined in claim 1, in whichthe thread-receiving passages through the thread guides are disposedsubstantially vertically, the clamping element is a ball, the firstcontrol means including means for creating a pressure differentialbetween the hollow defined by the adjacent ends of the thread guides anda fluid receiving chamber connected to a portion of one of the threadguides remote from the hollow, and the second control means includingmeans for momentarily connecting said chamber with the hollow to providea fluid stream impingeable on said ball.
 4. The clamp defined in claim1, in which the thread guides are disposed one above the other, and thethread-receiving passages are disposed substantially vertically, thelower thread guide having an upper inclined surface through which amouth of the thread-receiving passage through such guide opens, and theupper thread guide having a lower surface through which a mouth of thethread-receiving passage through such guiDe opens, having a conicaldepression, the axis of said depression being perpendicular to saidinclined surface of the lower thread guide.
 5. The clamp defined inclaim 1, in which the thread-receiving passage through each thread guideincludes a first passage portion remote from the clamping elementextending axially of its thread guide and a second passage portionhaving its axis inclined at an acute angle to the axis of its threadguide, the mouths of the inclined passage portions opening into thehollow between the thread guides and being offset from their respectivethread guide axes and being in substantial alignment.
 6. The clampdefined in claim 1, the first control means including pneumatic meansfor effecting relative axial movement of the thread guides away fromeach other against the force of the resilient means.
 7. The clampdefined in claim 1, further comprising a sleeve, mounting means rigidlyconnecting one thread guide in said sleeve, means connecting the otherthread guide with said sleeve for axial movement relative to said sleeveand said one thread guide and for conjoint rotation with said one threadguide and said sleeve, a first fluid-receiving chamber externally of thesleeve, a second fluid-receiving chamber between one thread guide meansand the sleeve, means connecting said first and second fluid-receivingchambers, and means for altering the pressure of fluid in said chambers.